This application is a national phase application of International Application No. PCT/JP98/05836, which was filed on Dec. 22, 1998 and which published in Japanese on Jul. 8, 1999, which in turn claims priority from Japanese Applications Nos. 367108/1997 filed Dec. 24, 1997, 71305/1998 filed Mar. 4, 1998, 89313/1998 filed Mar. 17, 1998, 340934/1998 filed Oct. 22, 1998, 340935/1998 filed Oct. 22, 1998, and 356858/1998 filed Nov. 9, 1998.
The present invention relates to improved transparent members for use as shields against electromagnetic waves and a process for producing such members. These transparent members are useful as shields against electromagnetic waves for use with electronic information devices such as plasma display panel, for example, for use as electromagnetic wave shield front filters for plasma display panel. The transparent members have excellent electromagnetic wave shield properties, produces no moire fringes and are excellent in visibility.
The electromagnetic waves produced by various electronic information devices and those to which such devices are exposed pose the problem of causing the devices to operate erroneously relative to one another and exerting an adverse effect on the human body. The methods of shielding against electromagnetic waves generally under study presently are divided into the following two methods.
One of these methods is a netting method wherein an electrically conductive fiber plated with nickel or copper over the surface is made into a net, which is sandwiched between two substrates or adhered to a substrate with an adhesive.
The other method is coating a substrate with a thin film of ITO (indium tin oxide), silver or the like over the entire surface thereof.
The netting method is generally excellent in electromagnetic wave shield properties, but is low in transparency. This method is further liable to produce moire fringes.
On the other hand, the coating method is satisfactory with respect to transparency and moire fringes but inferior in electromagnetic wave shield properties and especially low in shield properties in the high frequency band because of wavelength dependence.
In the case where the screen of the plasma display panel (PDP) or the like is viewed through an electromagnetic wave shield member, the shield member which must be transparent also needs to fulfill requirements as to visibility, i.e., to assure ease of viewing and not to cause much fatigue to the eyes, even if the screen is viewed therethrough over a prolonged period of time, whereas the two methods are still unsatisfactory in meeting the requirements.
An object of the present invention is to develop a shield member having higher transparency and higher electromagnetic wave shield properties.
Another object of the invention is to develop a shield member which is satisfactory in visibility and adapted to preclude or diminish occurrence of moire fringes.